In this project, we seek to 1) clarify and expand the nosology of the hereditary movement disorders; 2) contribute to the understanding of the underlying biochemical basis; 3) determine the most effective treatment and predictive testing for each disorder; and 4) suggest guidelines for counseling individuals at risk. General syndromes under study include the dystonias, tic disorders, the ataxias, and myoclonus. Approaches include standard epidemiologic and clinical and molecular genetics studies, and collaborative efforts in evaluating the role of neurotransmitters such as dopamine, and PET studies. We performed PET studies of at-risk members of two large kindreds with hereditary ataxia. Preliminary results suggested: a more generalized involvement than previously recognized; presymptomatic changes by PET; and evidence for genetic heterogeneity.